National Overview

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

U.S. Percentage Areas

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National Overview:

A strong west-to-east flow in the jet stream circulation characterized the weather pattern over the contiguous United States for December 2010. Deep low pressure systems developed in this flow, resulting in intense winter storms across the nation and outbreaks of cold Canadian air, especially east of the Rockies. About a third of the country was covered in snow at the beginning of the month. The snow cover expanded and contracted throughout the month with the passage of several winter storms, reaching 39 percent coverage by December 6th, about 53 percent by the 19th, and 55 percent by the 27th. By the end of the month, more than 8 feet of snow covered higher parts of the Sierra Nevada, with moisture content more than twice normal for this time of year. December 2010 was the 7th snowiest December for the contiguous U.S., based on satellite observations of area covered. The storm systems triggered deadly tornado outbreaks at the end of the month in the Midwest to Lower Mississippi Valley.

A pineapple express of moisture flowed into the U.S. from the Pacific for much of the month, bringing rain and snow to much of the West and northern Plains. Nevada and Utah had the wettest December in the 116-year record, Minnesota 4th wettest, North Dakota 5th wettest, and California ranked 7th wettest. Heavy rains brought drought relief to Hawaii, but the weather systems were deflected away from Alaska, which had a colder- and drier-than-normal December.

Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Two such large-scale atmospheric circulation patterns, which were dominant during November, continued in December. The first was the La Niña, which is the phenomenon created by cooler-than-average sea surface temperatures in the eastern tropical Pacific Ocean. La Niña is typically associated with wet conditions in the northern tier states and Ohio Valley this time of year, and warm and dry conditions in the southern tier states. The second atmospheric circulation index was the Arctic Oscillation (AO), which was negative during most of December and strongly negative during the last half of the month. A negative AO is typically associated with dry conditions in the Southeast (especially the southern Plains to Lower Mississippi Valley) and colder-than-normal temperatures east of the Rockies at this time of year (November-January).

The temperature and precipitation pattern for December 2010 matched what is expected from the negative Arctic Oscillation, especially east of the Rockies. Florida and Georgia had the coldest December in the 1895-2010 record and the Carolinas ranked 3rd coldest. A total of 11 states from the Ohio Valley to the Gulf Coast had the tenth coldest, or colder, December in 2010. Precipitation was below normal from the Southern Plains and Southeast to the southern Great Lakes, with Louisiana and Mississippi having the 3rd driest December and 4 other states ranking in the top ten driest category. As a result, drought expanded in the southern tier states, especially the southern Plains and Southeast. By the end of the month, 24 percent of the contiguous U.S. was classified in moderate to extreme drought, according to the U.S. Drought Monitor. The precipitation pattern over the West reflected a combination of La Niña and Arctic Oscillation influences.

Temperature Highlights

The national temperature, when averaged across the contiguous U.S., was near normal in December, only 0.4 degrees F (0.2 degrees C) below the long-term average.

Both Florida and Georgia experienced their coldest December on record. The average statewide temperature in Florida was more than 9 degrees F (5.0 degrees C) below the 20th century average, as every climate division in the state experienced an average December temperature that was record cold. In addition, several cities including — Miami, West Palm, Ft Lauderdale, Daytona, Orlando, Tampa, and Tallahassee — had thier coldest December on record.

The average temperature for several states in the West during the month of December was much above-normal. New Mexico had its second warmest December, both Colorado and Arizona had their fourth warmest, while it was Utah's eighth and Nevada's tenth warmest such December.

The cooler-than-normal temperatures can be traced back to the three-month period (October-December) in Florida, its 6th coldest such period. Three states had their eighth coldest October-December period: North Carolina, South Carolina, and Georgia. These below normal temperatures contributed to the Southeast climate region's ninth coldest such period.

Many of the contiguous states experienced an annual average temperature that was above the 20th century average. Only four states: Alabama, Florida, Georgia and Mississippi, had an average temperature that was below normal for the year. Of those, Florida's average temperature for the year was seventh coldest in 116 years, 1.3 degrees F (0.7 degrees C) below normal.

Several cities in the Northeast had their warmest year on record: Hartford, Connecticut; Boston, Massachusetts; Caribou, Maine; Concord, New Hampshire; Providence, Rhode Island.

Precipitation Highlights

Precipitation in December, when averaged across the contiguous U.S., was normal, only 0.01 inch (0.3 mm) below the 20th century average. Record precipitation amounts in the west were offset by the dryness in the southern Plains and Southeast.

The persistent on-shore flow from the Pacific contributed to the third wettest December for the West climate region. These dissipated by the time they reached the South and East, contributing to the second driest December in the South climate region.

In the South and East several states were drier-than-normal as both Mississippi and Louisiana experienced their third driest December on record. Elsewhere, Kansas had its sixth driest December, Alabama its seventh, Arkansas its eighth, and Delaware its tenth.

Precipitaton in the last quarter (October-December) was extreme for two states. Precipitation in Florida was 5.15 inches below normal resulting in its driest such period. The record dryness in Florida can be traced all the way back to the six-month period (July-December). Conversely, Nevada had its wettest October-December period on record with a statewide average of 3.44 inches (87.4 mm) above the normal. The persistent wetness in the East North Central (2nd wettest) and West (3rd wettest) climate regions can also be seen in the July-December period.

For the calendar year, precipitation was above normal for most climate regions, except for the South, Southeast and Central. The East North Central climate region had its third wettest annual period on record while its neighbor, the West North Central climate region, had its fifth wettest such period.

On the statewide level, precipitation averages are reflective of the active storm track across the upper tier states where North Dakota had its wettest calendar year on record. Iowa, Minnesota, and Wisconsin each had their second wettest year on record. It was also anomalously wet in South Dakota, which had it seventh wettest such period. Meanwhile, Louisiana experienced its fifth driest annual period and it was the ninth driest such period for Arkansas.

Other Items of Note

Tornado activity during December was above average with 59 preliminary reports. The December 31st outbreak across the Mississippi River Valley, with 49 preliminary tornado reports, was largest tornado outbreak during December on record. The previous record was 34 tornadoes on December 18, 2002.

Several large winter storms affected the U.S. during the month. According to data from the Rutgers Global Snow Lab, the December snow cover extent was the seventh largest on record for the continuos US. Several cities across the Midwest and Northeast broke monthly snowfall records including Minneapolis, Minnesota and Syracuse, New York.

Drought coverage continued to increased during December. The U.S. Drought Monitor reported 19.9 percent of the United States was affected by drought by December 28th. The wet conditions improved the drought conditions across Utah, Nevada, and California, while conditions worsened across southern Arizona and New Mexico. The drier than average weather across the Southern Plains worsened the drought in most of Texas and Oklahoma by one to three categories. Drought conditions also worsened for the Lower Mississippi River Valley, the Gulf Coast, and most of the Florida peninsula. Several weather systems moving through the Ohio River Valley improved drought conditions there one to two categories and ended drought in the central Appalachians.

Alaska Temperature and Precipitation:

Alaska
had its 16th coldest December since records began in 1918, with a temperature 6.8°F (3.8°C) below the 1971–2000 average.

Alaska
had its 43rd coldest October–December on record, with a temperature near the 1971–2000 average.

Alaska
had its 29th warmest year on record, with a temperature 0.7°F (0.4°C) above the 1971–2000 average.

Alaska
had its 21st driest December since records began in 1918, with an anomaly that was 30.6 percent below the 1971–2000 average.

Alaska
had its 31st wettest October–December on record, with an anomaly that was 2.5 percent above the 1971–2000 average.

Alaska
had its 28th driest year on record, with an anomaly that was 3.6 percent below the 1971–2000 average.

For additional details about recent temperatures and precipitation across the U.S., see the Regional Highlights section below. For information on local temperature and precipitation records during the month, please visit NCDC's Records page. For details and graphics on weather events across the U.S. and the globe please visit NCDC's Global Hazards page.

Temperatures during December 2010 averaged below normal for the first time since December 2009. The Northeast's monthly average of 25.4 degrees F (-3.7 degrees C) was 3.0 degrees F (1.7 degrees C) below normal and 2.4 degrees F (1.3 degrees C) cooler than December 2009. It was the coldest December in the region since 2000. Only Maine ended the month with warmer than normal temperatures; the state average of 24.2 degrees F (-4.3 degrees C) was 3.8 degrees F (2.1 degrees C) above normal. Negative temperature departures increased from north to south, with Vermont at 1.3 degrees F (0.7 degrees C) below normal, and West Virginia at 9.0 degrees (5.0 degrees C) cooler than normal. New Hampshire's average temperature was exactly normal. West Virginia's average temperature of 25.4 degrees (-3.7 degrees C) was only 3.7 degrees F (2.1 degrees C) warmer than the coldest year on record, 1989, making this December the 4th coldest since 1895. A cool December could not offset the previous eleven months of above normal temperatures. With an annual average of 49.2 degrees F (9.6 degrees C), 2010 became the 5th warmest year in the Northeast since recordkeeping began in 1895. Two states, New Hampshire and Rhode Island, had their warmest year on record. Of the remaining states, all but West Virginia had annual temperature averages that placed them in the top 20 warmest since 1895.

December's precipitation totals varied throughout the region, with 5 states averaging drier than normal and 7 states on the plus side. The regional average was 3.82 inches (97 mm), which was 113 percent of normal. Once again, Maine was the wettest state in the region, with 175 percent of the normal amount of precipitation. Delaware, with only 42 percent, had its 10th driest December since 1895. Annually, precipitation totals evened out, leaving the region at exactly 100 percent of normal. Yearly departures among the states ranged from 87 percent of normal in Delaware to 115 percent in Maine.

Two major weather events impacted the Northeast in December. A powerful storm drenched much of the region on the 1st and 2nd. In general, rainfall totals were in the 1 to 2 inch (25 to 51 mm) range, however parts of Pennsylvania, New York and West Virginia saw up to 4 inches (102 mm). Flash flooding resulted, closing roads and flooding homes, schools and businesses in the areas of heaviest rainfall. Strong winds accompanied the storm, with sustained winds in the 15-25 mph (6.7 - 11.1 m/s) range and peak gusts as high as 69 mph (30.8 m/s). The combination of wind and rain delayed fights and disrupted rail travel along the northeast corridor. The strong winds downed trees, branches and power lines, cutting power to thousands. One fatality was reported when a tree fell on a car in West Milford, NJ. The wind shift after the storm set up an intense lake effect snow band over western New York, burying the Buffalo area under 1 to 3 feet (30.5 - 91.4 cm) of snow in a narrow band downwind of Lake Erie. The following was taken from the Buffalo National Weather Service web site: "Snowfall amounts were incredible within the band. A general 30 to 40 inches (76-102 cm) fell in about a five-mile strip which ran from Lackawanna and southeast Buffalo, east northeast across northern West Seneca, south Cheektowaga, Depew and Lancaster over to Alden. Amounts dropped off steadily to the south, with about a foot (30 cm) in Orchard Park and less further south. The real story was the northern gradient though. Amounts dropped from two feet (60.9 cm) to a dusting in just a 3 or 4 mile (4-6 km) distance! This was evident along north-south roads like Transit and Harlem. For example, no measurable snow fell at Main and Harlem, but two feet (61 cm) at Walden and Harlem. The Buffalo Airport was right at the cutoff, with 2 inches (5.1 cm) at its northwest corner and a foot (30.5 cm) at its southeast corner! Further west, no snow fell in Buffalo at North St., 4 inches (10.2 cm) at City Hall and a foot (30.5 cm) at HSBC arena, probably the most remarkable gradient ever seen across the city! This event had major impact, not only in the 300,000 or so people affected, but from a major backup and shut down of the NYS Thruway from Exit 52 to 54, with hundreds stranded for almost 24 hours."

The second event was a blizzard that hit New Jersey and the New York City metro area on December 26 and tracked up the east coast, leaving significant snowfall in its wake. Totals of 6 to 12 inches (15-30 cm) covered New England, eastern New York and western New Jersey, with up to 2 feet (61 cm) in eastern New Jersey, metropolitan New York, and western New England. Holiday travel was severely impacted as flights were cancelled in to and out of LaGuardia, Kennedy and Newark airports, leaving travelers stranded at the airports for days. Driving was treacherous and clean-up kept residents close to home, leaving the malls empty, if they were able to open at all. ShopperTrak, an organization which records retail sales and customer traffic, estimated a retail loss for the two-day period at $1 billion. Municipalities affected by the blizzard took an extra financial hit as workers were paid double-time for plowing on Sunday. The storm could cost Danbury, CT as much as $450,000, which is more than half of their winter snow removal budget. The removal of Cranston, RI's 10-12 inches (25-30 cm) of snow could cost that city at least $150,000.

December temperatures were colder than normal across the Midwest. Departures from normal ranged from 0 degrees F (0 degrees C) in the upper Midwest to as much as 10 degrees F (6 degrees C) below normal in eastern Kentucky. Maximum temperatures were even colder ranging from 1 degrees F (1 degrees C) to 14 degrees F (8 degrees C) below normal. Kentucky recorded its first colder than normal month since February of this year. 2010 was near normal for most of the Midwest with only the northern parts of Minnesota, Wisconsin, and Michigan averaging 2 degrees F (1 degrees C) to 4 degrees F (2 degrees C) above normal.

Midwest precipitation totals varied widely in December. Above normal precipitation fell in the northwest quarter of the region with west-central Minnesota receiving nearly five times their normal precipitation. Eastern Kentucky was also slightly above normal. The areas between received less than normal precipitation with a swath from Missouri to Lake Huron at less than half of their normal. Snowfall was especially heavy in Minnesota, western Wisconsin, and northeast Iowa. Above normal snowfall also fell along a narrow swath extending from southern Minnesota to eastern Kentucky. Three different storms tracked along this path during the month. Cooperative stations in Michigan (6) and Wisconsin (1) reported 48 inches (122 cm) or more of snow in December and many more in Minnesota (20) and Michigan (5) reported snowfall totals of 36 inches (91 cm) to 48 inches (122 cm). Stations in Iowa (4), Michigan (4), and Minnesota (18) reported snow depths of at least 24 inches (61 cm) at some point during the month. 2010 annual precipitation was above normal for most of the western half of the Midwest with south-central Iowa more than 20 inches (508 mm) above their normal for the calendar year. Southeast Missouri and along the Ohio River to Cincinnati were 6 inches (152 mm) to 10 inches (254 mm) below normal for their 2010 annual precipitation.

Among the numerous winter storms during December was the blizzard that affected much of the Midwest on the 11th and 12th. Heavy snow fell in the northern half of the region and strong winds whipped up blizzard conditions for the northern two-thirds. Airline, train, and auto travel were interrupted across the Midwest. More than a dozen deaths were blamed on the storm, mostly related to automobile accidents. Interstate highways were closed for a time in Minnesota, Wisconsin, Iowa, and Illinois and even snowplows and rescue crews were pulled off the roads due to dangerous conditions. Strong winds blew as far south as Table Rock Lake in southern Missouri where a boat with 600+ people on board was blown ashore. The boat remained grounded overnight waiting for waves and winds to decrease before it could safely return to its dock.

Nineteen tornadoes touched down in Missouri and Illinois on December 31. The 17 tornadoes in Missouri set a state record for December. Four people died in two fatal Missouri twisters, one near Lecoma and the other near Rolla. Nearly 300 structures were damaged and 50 were destroyed by the tornadoes that were rated from EF0 to EF3 on the Enhanced Fujita scale.

Monthly average temperatures for December 2010 were well below normal across the Southeast region. The greatest departures occurred throughout Florida and eastern sections of Georgia, the Carolinas, and Virginia, where monthly average temperatures were 9 to 11 degrees F (5.0 to 6.1 degrees C) below normal. Interior portions of the Southeast were generally 6 to 9 degrees F (3.3 to 5.0 degrees C) below normal, while much of Alabama and northern Virginia were 5 to 6 degrees F (2.8 to 3.3 degrees C) below normal. Over 70 locations in the Southeast experienced their coldest December on record, including Brunswick, GA, Cape Hatteras, NC, and Mount Mitchell, NC, as well as all major metropolitan area in Florida except Pensacola (3rd coldest). December ranked among the top 5 coldest in many other locations across the region, including Asheville, NC, Charlotte, NC, and Charleston, SC (2nd coldest); Savannah, GA, Raleigh-Durham, NC, and Norfolk, VA (4th coldest); and Columbus, GA, Columbia, SC, and Roanoke, VA (5th coldest). Across the Southeast, over 1,100 daily low maximum temperature records and over 800 daily minimum temperature records were tied or broken during the month. Jacksonville, FL recorded 19 days of subfreezing minimum temperatures during the month, which shattered the old record of 12 set back in 2000. The frigid air masses that predominated across the Southeast also influenced parts of the Caribbean; monthly average temperatures were below normal across Puerto Rico and as much as 4 degrees F (2.2 degrees C) below normal on the U.S. Virgin Islands.

Monthly precipitation was below normal (generally less than 50 percent) across nearly the entire region in December. A large portion of the monthly rainfall came on the 1st of the month as a line of strong storms moved through the Southeast and mid-Atlantic regions. Most notably, Brevard, NC, recorded a monthly record 24-hr rainfall of 6.55 inches (166.4 mm), breaking the old record by over two inches (50.8 mm). The driest locations across the Southeast (less than 25 percent of normal) were found in central and eastern Florida, southern Alabama, central portions of Georgia and the Carolinas, much of the southern Appalachian Mountains, and the Shenandoah Valley of Virginia. Sanford, FL, located northeast of Orlando, recorded 0.15 inches (3.8 mm) of precipitation for the month, which was only six percent of normal. Montgomery, AL [1.03 inches (26.2 mm)], and Columbus, GA [1.56 inches (39.6 mm)], experienced their 2nd driest December in records extending back to 1871 and 1947, respectively. In contrast, monthly precipitation totals were between 150 and 300 percent of normal across the northern coast of Puerto Rico. San Juan, PR, recorded 7.47 inches (189.7 mm) of precipitation for the month, which was 2.9 inches (73.7 mm) above normal.

The calendar year 2010 was exceptionally warm in the northern tier of the region. Most notably, the Washington D.C. area recorded its 4th warmest year ever in a record extending back to 1871. Conversely, it was an exceptionally cold year in the southern tier of the region, as 12 locations in Florida experienced their coldest year on record, including the Miami Beach area. It was the 3rd coldest year ever in the Jacksonville, FL and Vero Beach, FL areas, the 4th coldest year in the Key West, FL area, and the 5th coldest year ever in the Gainesville, FL area. With respect to precipitation, it was the driest year on record in the Jacksonville Beach, FL area with a preliminary annual total of 28.44 inches (722.4 mm). Conversely, San Juan, PR, recorded its wettest year on record with 89.51 inches (2274 mm), eclipsing the previous record of 87.55 inches (2224 mm) set in 1931.

There were only five reports of severe weather across the Southeast in December. On the 11th of the month, strong winds brought down numerous trees and knocked over fences in Santa Rosa, FL (north of Pensacola) and damaged school buses at a middle school about 30 miles away in Baldwin, AL. Felled trees and structural damage were reported in northwest Alabama following a line of strong storms on the 31st of the month. No tornadoes were reported across the Southeast in December.

December was an active month for winter weather across much of the Southeast. On the 4th and 5th of the month, an area of low pressure moving through the Mississippi River and Ohio River Valleys produced 1 to 3 inches (25.4 to 76.2 mm) of snow across central portions of North Carolina and Virginia, while higher elevations in the southern Appalachian Mountains received over 8 inches (203.2 mm). Charleston, SC reported flurries on the 8th of the month as a weak upper-level disturbance moved across the region. On the 15th and 16th, a storm system moving through the Tennessee River Valley produced 1 to 4 inches (25.4 to 101.6 mm) of snow across much of central North Carolina and eastern Virginia. Ice accumulations of 0.12 to 0.25 inches (3.0 to 6.4 mm) were also reported in western parts of the Carolinas and north Georgia (including Atlanta). Snowfall was observed across a large part of the region on the 25th and 26th, as a strengthening cyclone moved northeastward along the Gulf and Atlantic coasts. The greatest amounts from this storm were recorded in the southern Appalachian Mountains and eastern sections of North Carolina and Virginia, where Flat Springs, NC and Norfolk, VA received 17.8 and 13.4 inches (452.1 and 340.4 mm), respectively. Central and northern portions of Alabama, Georgia, and South Carolina received 2 to 6 inches (50.8 to 152.4 mm). Remarkably, snow flurries and graupel were reported as far south as Lakeland, FL (east of Tampa). For many locations across the region, including Huntsville, AL, Macon, GA, Raleigh-Durham, NC, and Richmond, VA, it was the first "White Christmas" in many decades. In other locations, such as Atlanta, GA, it was the first "White Christmas" ever recorded. With respect to monthly snowfall totals, Boone, NC recorded 28.7 inches (729.0 mm), which broke the old record of 23.3 inches (591.8 mm) set back in 1969. Norfolk, VA recorded 17.8 inches of snow (452.1 mm), which registered as the 2nd snowiest December in a record extending back to 1874.

Despite the overall lack of precipitation during the month, the coverage of drought conditions (D0 or greater according to the U.S. Drought Monitor) across the Southeast decreased from 87 percent at the end of November to 77 percent at the end of December. Areas of abnormal dryness (D0) were eliminated across parts of Virginia, western and eastern North Carolina, western Alabama, and northeast Georgia. In addition, moderate drought (D1) conditions expanded slightly into parts of central North Carolina and south Florida, while extreme drought (D3) conditions expanded across northeast Florida and southeast Georgia. The cold temperatures severely disrupted the planting of winter vegetables (e.g. peppers and onions) in parts of Florida and Georgia and resulted in a state of emergency declaration in Florida to ensure that the harvesting and transport of fall crops were not delayed on account of the cold weather.

Temperatures across the High Plains Region this month were below normal in the eastern half and above normal in the western half. The dividing line between the above and below normal temperatures ran from southwestern South Dakota into central Nebraska, and then into west-central Kansas. December temperature departures ranged from 7 degrees F (3.9 degrees C) below normal in North Dakota to 10 degrees F (5.6 degrees C) above normal in Colorado. Great Sand Dunes National Park in Colorado recorded its warmest December with an average temperature of 31.0 degrees F (-0.6 degrees C) which was 8.0 degrees F (4.4 degrees C) above normal. This just surpassed the old record of 30.9 degrees F (-0.6 degrees C) which occurred in 1977 (period of record 1950-2010). Cortez, Colorado also had its warmest December on record with an average temperature of 36.7 degrees F (2.6 degrees C). This broke the old record of 36.3 degrees F (2.4 degrees C) which was set in 1980 (period of record 1911-2010).

Southern portions of the Region including Kansas, Nebraska, and eastern Colorado received little to no precipitation this month. This caused existing drought conditions to persist and led to the development of drought in eastern Kansas as well. While the southern portion of the Region remained dry, several storm systems impacted the northern portions of the Region this month. The Dakotas were hit particularly hard by heavy snowfall which set new records and impacted travel. Several areas of both North Dakota and South Dakota had liquid equivalent precipitation totals which were over 400 percent of normal. One location which set many records this month was Williston, North Dakota. Williston had its 3rd wettest December on record with 1.95 inches (50 mm) of liquid equivalent precipitation (period of record 1894-2010). The current record held with 2.50 inches (64 mm) recorded in 2008. It also recorded its snowiest December with 35.3 inches (90 cm) of snow (period of record 1962-2010). 14.3 inches (36 cm) of this total fell on December 10th and set the highest one-day total snowfall record for December. The old record of 11.4 inches (29 cm) was also set in 2008. Later in the month, on December 21st, a new December snow depth record of 23.0 inches (58 cm) was also set.

According to the U.S. Drought Monitor, drought conditions deteriorated across the southern portions of the Region this month. By the second week of December abnormally dry conditions (D0) had expanded north from Oklahoma into eastern Kansas and severe drought conditions (D2) had expanded from eastern Colorado into western Kansas. In addition, D0 had spread further east in Nebraska. By the end of the month moderate drought conditions (D1) had developed in eastern Kansas as well. Only slight improvements were seen in extreme northwestern Colorado where the D0 area was eliminated and in western Wyoming where the D1 and D0 areas were trimmed due to heavy snowfall. According to the U.S. Seasonal Drought Outlook released December 16th drought conditions across Colorado, Kansas, and Nebraska were expected to persist and the D1 area in Wyoming was expected to improve.

December average daily temperatures varied spatially throughout the Southern Region, with a strong gradient from west to east. The western states experienced a slightly warmer than normal month, while eastern and central states experienced a much cooler than normal month. In, Tennessee, the state average daily temperature for the month was 32.70 degrees F (32.7 degrees C), which was the sixth coldest December on Record (1895-2010). It was also quite colder than normal in Mississippi, which recorded its eighth coldest December on record (1895-2010) with a state average temperature of 41.80 degrees F (5.44 degrees C). Louisiana and Arkansas reported their 16th and 17th coldest December on record, respectively. The state monthly average temperature for the month in Louisiana was 47.80 degrees F (8.78 degrees C). In Arkansas, the state average monthly temperature was 38.60 degrees F (3.67 degrees C). The warmest areas of the region included much of western Texas and western Oklahoma, where counties experienced average daily temperatures that ranged from 2 to 6 degrees F (1.11 to 3.33 degrees C) above the climatological normal.

December precipitation totals were quite low over most the Southern Region. For the majority of the region, this is the third consecutive dry month. In December, the majority of the region received less than half of the monthly normal precipitation. Louisiana reported a state average monthly total of only 1.85 inches (46.99 mm), which is the third driest December on record (1895-2010). Likewise, Mississippi experienced its third driest December on record (1895-2010) with a monthly precipitation total of only 1.45 inches (36.83 mm). Arkansas also reported a monthly precipitation total of 1.45 inches (36.83 mm), which makes it their eighth driest December on record (1895-2010). Texas recorded its eleventh driest December (1895-2010), with a monthly precipitation total of 0.67 inches (17.01 mm). Tennessee reported its eighteenth driest December, while Oklahoma reported its thirty-first driest December (1895-2010). The state average precipitation total in Tennessee was 2.76 inches (70.10 mm), while Oklahoma reported a value of 0.93 inches (23.62 mm). The driest areas of the Southern Region included much of western Texas, southern Texas, northern Louisiana, and southern Arkansas. In these areas, most stations reported less than a quarter of the monthly normal precipitation totals. In the case of west and southern Texas, many stations recorded less than one tenth of an inch (2.54 mm) for the month.

A third consecutive month of dry conditions in the Southern Region has resulted in a wide expansion of drought conditions. As of December 28, 2010, 67.65 percent of the Southern Region is now experiencing moderate drought or worse; 35.21 percent is in severe drought or worse, and 10.17 percent is classified as extreme drought conditions. This is a dramatic change from last month. For instance, on November 30, 2010, the aforementioned values were 41.2 percent, 19.3 percent, and 2.7 percent, respectively. The most significant changes are seen in the central counties of eastern Texas where extreme drought has been introduced. There was also a westward expansion of severe drought into the western parishes of Louisiana.

Except for Montana, nearly the entire West observed above normal temperatures, especially SE New Mexico and the Front Range of Colorado. Alamosa, CO, tied its warmest December on record going back 63 years while Grand Junction, CO, had its warmest December since 1980. Fairbanks, AK, on the other hand, had its coldest December since 1980. Had it not been for extremely cold temperatures the final two days of the month many other locations would probably have broken records for December warmth. Arizona recorded an unofficial new state record for the coldest all time December temperature when an automated weather station near Flagstaff recorded -37 F (-38.3 C) on final hour of the 31st, breaking the old state record of -36 F (-37.8 C).

Precipitation was well above normal throughout the region except for Southern Arizona and New Mexico and Eastern Colorado. Many parts of southern and central California received their wettest December ever. It was the second wettest December on record in downtown Los Angeles dating back to 1889. Bishop, CA, received 105% of their annual average in 3 days (18-20th). Up to 29 inches of rain in the San Gabriel and San Bernardino Mountains of Southern California for the month, most of it within a 6-day period from the 17th-22nd. Bakersfield's (CA) total of 5.82 inches (148 mm) not only broke a December record but an all time monthly record going back to 1893. New December records were also set in portions of Southern Nevada and Utah. St. George UT had their wettest December on record dating back 117 years. Over 15 inches (381 mm) of precipitation fell at Mt. Charleston, NV, while Ely NV recorded their wettest and snowiest December in 85 years of data. Snowpack in the Sierra Nevada of California and a broad swath northeast to the upper Colorado River Basin was over 200% of normal by the end of the month, and the rest of the West except Washington was reporting a snowpack of well over 100%. Meanwhile, in Honolulu, rainfall for the December was the greatest since 1987 (11.73 inches, 298 mm) and provided 67% of their 2010 annual total. Much of that fell in one day (5.41 inches, 137 mm) on the 19th.

December 11-14: Heavy Rain and Strong Winds in Washington: A very warm and moist storm hit the Pacific Northwest. Rainfall totals were between 3 and 8 inches (76-203 mm) in NW Washington with some isolated areas of the Olympic Peninsula measuring up to 12 inches (305 mm). Localized urban and small stream flooding occurred, and service on Amtrak was cancelled from Portland, OR, to Vancouver, Canada, for nearly 48 hours due to numerous landslides. A 55-year old woman was killed in the early morning hours of the 14th near Port Orchard, WA, when strong winds toppled a tree on to her house while she slept.

December 17-22: Heavy Rain and Snow in California: Beginning on Friday the 17th one of the more powerful Pacific storms to hit California and the Southwest in the past six years caused extensive damage throughout the region. Six days of heavy rain triggered rock and mud slides, large scale flooding, evacuations and road closures throughout the four states of California, Nevada, Utah and a portion of Arizona. In Southern California, a 20-mile stretch of Highway 1 between Malibu and Oxnard was closed on the 21st after a rock and mud slide. Amtrak service was also disrupted between San Diego and San Juan Capistrano due to mudslides and flooding. As many as 70 homes were buried in over four feet of mud near San Bernardino and over 200 homes were evacuated. One death was confirmed in Riverside County when a woman who drove into a flooded crossing was swept away. According to AAA, more than 25,000 motorists called for help on the 20th, the largest number ever in a 24-hour period. A state of emergency was declared for 6 counties in southern California and damage is estimated at over $10 million. In Mission Valley, near San Diego, 900 residents were forced from their homes from flooding. In Southern Nevada, Northwest Arizona and Southwest Utah record rainfall and flooding occurred over the region. Six homes were swept away in Beaver Dam Wash, AZ, with another six suffering severe damage. The Virgin and Santa Clara Rivers flooded, destroying several holes of the Southgate Golf Course in St. George. Significant rockfalls in Zion National Park forced a closure of the park. Several roadways and intersections in Las Vegas were closed due to flooding.

December 29-31: Strong Winter Storm: A strong cold front moved through the entire West on the final three days of the month causing very cold temperatures, heavy snow and strong winds. Two feet of snow and 100 mph winds were recorded in the Sierra Nevada followed by an extreme drop in temperature. A snowboarder died from exposure when she got lost at a California ski area. Local flooding from heavy rain was reported in southwest Oregon and southern California. A 70-year old woman was killed at the Safari West Preserve near Santa Rosa, CA, when an oak tree was uprooted and fell on the frame tent she was staying in.

PLEASE NOTE: All of the temperature and precipitation ranks and values are based on preliminary data. The ranks will change when the final data are processed, but will not be replaced on these pages. Graphics based on final data are provided on the Temperature and Precipitation Maps page and the Climate at a Glance page as they become available.

Global Analysis

Contents of this Section:

Global Highlights

The combined global land and ocean average surface temperature for December 2010 was 0.37°C (0.67°F) above the 20th century average of 12.2°C (54.0°F). This tied with 1982 and 1994 as the 17th warmest December on record. It was the coolest December since 2000.

The global land surface temperature for December 2010 was 0.38°C (0.68°F) above the 20th century average of 3.7°C (38.7°F). This tied with 1994 as the 30th warmest December on record.

The worldwide ocean surface temperature for December 2010 tied with 1994 and 1998 as the tenth warmest December on record, 0.36°C (0.65°F) above the 20th century average of 15.7°C (60.4°F).

For the year (January–December), the combined global land and ocean surface temperature tied with 2005 as the warmest such period on record, at 0.62°C (1.12°F) above the 20th century average of 13.9°C (57.0°F). 1998 is the third warmest year-to-date on record, at 0.60°C (1.08°F) above the 20th century average.

Please Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective with the July 2010 State of the Climate Report, NCDC transitioned to the new version (version 3b) of the extended reconstructed sea surface temperature (ERSST) dataset. ERSST.v3b is an improved extended SST reconstruction over version 2. For more information about the differences between ERSST.v3b and ERSST.v2 and to access the most current data, please visit NCDC's Global Surface Temperature Anomalies page.

Introduction

Temperature anomalies for December 2010 are shown on the dot maps below. The dot map on the left provides a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) dataset of land surface stations using a 1961–1990 base period. The dot map on the right is a product of a merged land surface and sea surface temperature (SST) anomaly analysis developed by Smith et al. (2008). For the merged land surface and SST analysis, temperature anomalies with respect to the 1971–2000 average for land and ocean are analyzed separately and then merged to form the global analysis. For more information, please visit NCDC's Global Surface Temperature Anomalies page.

December

The combined global land and ocean surface temperature for December 2010 tied with 1982 and 1994 as the 17th warmest December since records began in 1880, at 0.37°C (0.67°F) above the 20th century average. This was the coolest December on record since 2000. The Southern Hemisphere combined global land and ocean surface temperature was also the 17th warmest December on record, while the Northern Hemisphere combined global land and ocean temperature was the 20th warmest.

The worldwide land surface temperature tied with 1994 as the 30th warmest December on record, at 0.38°C (0.68°F) above the 20th century average of 3.7°C (38.7°F). A large-scale climate pattern—the Arctic Oscillation—influenced land surface temperatures across parts of the Northern Hemisphere during the month. The Northern Hemisphere December land temperature tied with 1923 and 1973 as the 34th warmest on record, while the Southern Hemisphere land temperature tied with 1980 as the 22nd warmest December on record. More than two-thirds of the Earth's land mass is located in the Northern Hemisphere.

The El Niño-Southern Oscillation (ENSO) is a periodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean, affecting weather patterns in many parts of the world. In December, a moderate-to-strong cold phase (La Niña) ENSO persisted as sea surface temperaures in the eastern and equatorial Pacific Ocean remained cooler than normal. The December 2010 worldwide averaged ocean temperature tied with 1994 and 1998 as the tenth warmest on record, 0.36°C (0.65°F) above the 20th century average of 15.7°C (60.4°F). The Northern Hemisphere ocean temperature was the ninth warmest on record and the Southern Hemisphere ocean temperature tied with 1979, 1999, and 2000 as the 17th warmest on record. According to NOAA's Climate Prediction Center (CPC), La Niña is expected to peak during the end of 2010 into early 2011 and last at least into the Northern Hemisphere spring 2011 with a lesser intensity.

Across the globe, the warmest temperature anomalies during December 2010 were present across most of north-central and eastern Canada, far eastern and southwestern Russia, and southeastern Europe. The coolest temperature anomalies were located in northern and western Europe, central Russia, southern Alsaka, much of the eastern United States, interior Australia, and most of the eastern and central Pacific Ocean.

Regionally, a strong negative phase of the Arctic Oscillation brought cooler-than-average temperatures to large portions of the Northern Hemispere land areas. The United Kingdom's temperatures were, on average, about 5°C (9°F) below the 1971–2000 average during the month of December, making it the coldest December in more than 100 years, according to the UK Met Office. It was also the coldest month recorded since February 1986. To the west, Germany's national meteorological service, Deutscher Wetterdienst, reported that the country had its fourth coldest December since reliable records began in 1881 and coldest since 1969, with temperatures 4.5°C (8.1°F) below the 1961–1990 average. The contiguous United States as a whole experienced its seventh largest December snow cover extent (with records dating back to 1966), and the Southeast had its third coldest December on record. The negative Arctic Oscillation also contributed to the lowest December Arctic sea ice extent on record, according to the National Snow and Ice Data Center. The low sea ice conditions occurred in regions where the ice coverage would typically expand this time of year; however, above-normal temperatures were recorded in these areas.

ENSO also impacted temperature patterns toward the end of 2010. According to the Australian Bureau of Meteorology, La Niña influenced the precipitation patterns over Australia during the latter part of the year. Heavy rainfall across the country brought cooler temperatures, leading to the country's second coolest December on record, behind 1999. The average temperature across Australia for the month was 1.35°C (2.43°F) below normal.

The average position of the upper-level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the December 2010 map, respectively) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products, please see the Climate Monitoring Global Products page.

Year-to-date (January-December)

The 2010 calendar year (January–December) map of temperature anomalies shows that warmer-than-average temperatures occurred during 2010 over most of the world's surface. The warmest annual above-average temperatures occurred throughout the high latitude regions of the Northern Hemisphere, Canada, Alaska, the equatorial Atlantic Ocean, the Middle East, eastern Europe, and northern Africa. Temperatures were notably cooler across the Southern oceans, most of the eastern Pacific Ocean, western Scandinavia, part of central Russia, and parts of Australia. The combined global land and ocean surface temperature for the year tied with 2005 as the warmest January–December period on record. This value is 0.62°C (1.12°F) above the 20th century average. Please refer to the NCDC State of the Climate Annual Global Anaysis report for more detailed information.

Images of sea surface temperature conditions are available for all weeks during 2010 from the weekly SST page.

* Global Land tied with 1994 as 30th warmest on record. * Global Ocean tied with 1994 and 1998 as 10th warmest on record. * Global Land and Ocean tied with 1982 and 1994 as 17th warmest on record. * Northern Hemisphere Land tied with 1923 and 1973 as 34th warmest on record. * Southern Hemisphere Land tied with 1980 as 22nd warmest on record. * Southern Hemisphere Ocean tied with 1979, 1999, and 2000 as 17th warmest on record.

* Global Land tied with 2005 as the 2nd warmest year on record. * Global Ocean tied with 2005 as the 3rd warmest year on record. * Global Land and Ocean tied with 2005 as the warmest year on record. * Northern Hemisphere Ocean tied with 2003 as the 3rd warmest year on record. * Southern Hemisphere Land tied with 2003 as the 5th warmest year on record.

Precipitation

The maps below represent anomaly values based on the GHCN dataset of land surface stations using a base period of 1961–1990. During December 2010, above-average precipitation fell over areas that included eastern Australia, most of Central America, much of the western third of the United States, much of eastern Asia, northwest China, Kenya, and Tanzania. Drier-than-average conditions were present across most of the eastern two-thirds of the United States, northern Africa, much of the Middle East, and most of southern South America.

La Niña brought record rainfall to most of Australia toward the end of the year. The country had its wettest spring (September–November; Northern Hemisphere fall) on record. With extreme wetness in December—particularly in the northeastern state of Queensland, which had its wettest December on record and experienced major flooding—the average precipitation across the country was 99 percent above normal for the month, ranking as Australia's second wettest on record, behind December 1975.

December brought extremely variable precipitation to China. According to the China Meteorological Administration, the provinces of Inner Mongolia, Xinjiang, and Heilongijang experienced their wettest December on record, with national records dating back to 1961, while Jilin, Jianxi, and Hunan had their second wettest on record. However, precipitation was 30–80 percent below normal across most of northern China, Huaghuai, Jianghuai, and Shaanxi, enhancing drought conditions in those areas.

Year-to-date (January-December)

Global precipitation in 2010 was well above the 1961–1990 average, ranking as the wettest on record since 1900. Precipitation throughout the year was variable in many areas. Regionally, drier than average conditions were widespread across much of French Polynesia, the Solomon Islands, Hawaiian Islands, northwestern Canada, extreme northwest and northeast Brazil, and southern Peru. The wettest regions induded most of Central America, much of India, southwestern China, east Asia, Borneo, and parts of Australia. Please refer to the NCDC State of the Climate Annual Global Anaysis report for more detailed information.

Global Hazards

Please note: Material provided in this report is chosen subjectively and included at the discretion of the National Climatic Data Center (NCDC). The ability to report on a given event is limited by the amount of information available to NCDC at the time of publication. Inclusion of a particular event does not constitute a greater importance in comparison with an event that has not been incorporated into the discussion. Data included in this report are preliminary unless otherwise stated. Links to supporting information are valid at the time of publication, but they are not maintained or changed after publication.

Updated 14 January 2011

DecemberCentral Somalia was in the midst of a severe drought read moreDecember 2ndThe largest fire in Israel's history broke out near Haitha read moreEarly DecemberThe worst floods in more than a century impact the Balkans read moreEarly DecemberWeeks of torrential rains wreak havoc across Colombia, Venezuela, and Panama read moreDecember 11th–12thStrong storms produce record rainfall in the northwestern U.S. read moreDecember 17th–22ndCalifornia receives record rain and snowfall read moreDecember 7thAdelaide, Australia experienced its wettest December day on record read moreDecember 11th–12thA powerful cyclone tore across the eastern Mediterranean and the Middle East read moreDecember 1stA strong storm system wreaked havoc across the northeastern U.S. read moreDecemberNorthern Europe experienced heavy snow, ice, and arctic temperatures read moreDecember 10th–13thA blizzard affected the miswestern U.S. and southern Ontario, Canada read moreDecember 15thA mixture of snow, sleet, and freezing rain brought treacherous conditions to the southeastern U.S. read moreDecember 25thTropical Cyclone Tasha soaks waterlogged Queensland, Australia read moreDecember 25th–27thLarge-scale snow storm impacts eastern United States read moreDecember 31stEight people were killed by tornadoes in south-central United States read more

During the last three months of 2010, rainfall in eastern China's Shandong province was 86 percent below average, receiving only 0.35 inches (9 mm) of rain. The lack of precipitation during this period enhanced drought conditions, resulting in the worst drought in 50 years for the region and leaving about 240,000 people without adequate drinking water. In addition, about 1.84 million hectares of cropland was affected by the drought. To the west, Shanxi province received 0.07 inches (1.7 mm) of rain, 89 percent below average.

A forest fire—thought to be the largest in Israel's history—broke out in the Carmel Mountains near Haifa in the northern part of the country on December 2nd. Fueled by high winds and dry conditions, at least 41 people were killed after a bus burst into flames and 17,000 were evacuated as the fire destroyed more than 12,300 acres (5,000 hectares) of land, including an estimated five million trees and 74 buildings. The fire was declared to be "under control" on December 5th, after 24 aircraft, including the world's largest firefighting aircraft—a Boeing 747 Evergreen SuperTanker—were brought in to help battle the blaze.

A week of copious rainfall brought flooding to the Balkans during the first week in December. More than 12,000 people were evacuated in northern Albania and 35,000 acres (14,000 hectares) of farmland were destroyed. Locally, the River Drina rose to its highest level in more than a century. Authorities were forced to open emergency dam gates and release the water into the Shkodra lake, which, along with the rainfall, caused the flooding. Streets in the town of Shkodra were inundated with six and a half feet (two meters) of water. The only ways into or out of town were by boat or helicopter. Bosnia, Serbia, and Montenegro declared a state of emergency—the River Drina runs along the borders of all three countries. In northern Bosnia, the heavy rains triggered a landslide in the city of Tuzla that killed three people. In southern Croatia, the River Neretva reached its highest level in 50 years, flooding 700 homes in the town of Metkovic.

Weeks of torrential rainfall in Central and South America heavily impacted Venezuela, Colombia, and Panama. The heavy rains caused flooding and landslides that killed at least 34 people in Venezuela and caused more than 100,000 to flee their homes. The country's Caribbean coast was particularly hard hit. In Colombia, a landslide on December 5thkilled at least 47 people and left an estimated 80 others missing in the city of Medellin in Antioquia province. The landslide was a product of Colombia's heaviest rains since record keeping began in 1969. Heavy rainfall and flooding in Panama killed 10 people and damaged over 2,500 homes. The downpours forced the Panama Canal to close on December 8th and 9th, the first time the canal closed due to weather conditions since its opening in 1914. The rainy season was particularly severe this year. The extreme conditions were attributed to the La Niña climatic phenomenon, where cooler-than-normal temperatures in the equatorial and central Pacific Ocean impact weather conditions in various parts of the world.

The "Pineapple Express"—a meteorological event where southwest winds bring warm, moist air to the U.S. West Coast—produced record rainfall to the Pacific Northwest during December 11th–12th. Seattle experienced record daily rainfall two days in a row. The Seattle-Tacoma International Airport recorded 1.42 inches (36 mm) of rain on the 11th, breaking the old daily record of 1.32 inches (34 mm) set in 1955. The next day, 2.19 inches (56 mm) fell, breaking the daily record of 1.70 inches (43 mm) set in 1966. The Stillaguamish River in western Washington state reached 21.06 feet (6.42 meters) at Arlington, tying the record set in November 2006. Flood stage for the river is 14 feet (4.3 meters). The storm system also brought record warmth to the area. On December 14th, the temperature at Seattle-Tacoma International Airport reached 57°F (13.9°C), breaking the old daily record of 55°F (12.8°C) set in 2004.

More storms—courtesy of the Pineapple Express—inundated California with rain and snow on December 17th–22nd. The week-long event brought average rainfall of 5–10 inches (125–250 mm) in coastal and valley areas of southwestern California and 10–18 inches (250–460 mm) to the nearby foothills and mountains. A total of 24.70 inches (627 mm) of rain was reported at Tanbark in Los Angeles County. Los Angeles International Airport—among several other locations—broke its daily precipitation record on both the 19th (2.23 inches [57 mm], surpassing the old record of 1.62 inches [41 mm] set in 1984) and the 20th (0.98 inches [25 mm], surpassing the previous record of 0.7 inches [18 mm] set in 1952). In addition to breaking its daily precipitation record of 2.80 inches (71 mm) on the 19th, besting the old record of 2.12 inches (54 mm) set in 1921, downtown Los Angeles (a different area than Los Angeles International Airport) recorded a total of 8.16 inches (207 mm) of rain during from the 15th–22nd, with almost all of the rainfall occurring during the latter five days. For the month, downtown Los Angeles experienced its second wettest December on record, with 10.23 inches (260 mm) total. Many other locations had their all-time wettest Decembers, including Los Angeles International Airport (8.83 inches [224 mm]), Long Beach Airport (10.41 inches [264 mm], and Oxnard (9.16 inches [233 mm]). Generally, rainfall was 300–600 percent above normal for the month in this region. Flooding and mudslides occurred in some areas, leading to the evacuation of 400 residents in San Juan Capistrano after a hillside collapse. The governor of California also declared a state of emergency in six counties. Fortunately no fatalities related to the storms were reported. Additionally, 208 inches (528 cm) of snow reportedly fell throughout the month at Mammoth Mountain ski resort, becoming the snowiest December on record at the resort since records began 1969; the old record was 139.8 inches (355 cm) set in 1971.

After weeks of heavy rainfall, Australia's attorney general declared 45 communities in eastern Australia disaster areas on December 9th. Four people were killed and thousands were forced to evacuate their homes as rivers overflowed their banks and caused major flooding. The worst weather, however, was reported to be in South Australia, where Adelaide had its wettest December day on record on the 7th. Almost two weeks later, on the 20th, 9.65 inches (245 mm) of rain fell over Carnarvon, a town located about 560 miles (900 km) north of Perth in Western Australia. Local media reported that the area experienced its worst flooding in 50 years. The Gascoyne River reached its highest levels ever recorded, breaking the previous record set in 1960. Please see the Tropical Cyclones section for information on the flooding effects in northeastern Australia due to Tropical Cyclone Tasha.

Torrential rains occurred during the last week in December in southern Egypt. Strong flood currents swept away a bus driving along a highway more than 100 miles (160 km) south of Cairo, killing 15 people. Further to the east, in Jeddah, Saudi Arabia—the country's second largest city—waist-high water flooded city streets, damaging homes and disrupting traffic.

A strong storm system tore across the northeastern U.S. at the beginning of December. The storm, which spawned 11 tornadoes in the southeastern U.S. states of Alabama, Georgia, and South Carolina on November 30th, according to preliminary data from NOAA's Storm Prediction Center, barreled toward the Northeast. On December 1st, wind gusts as high as 70 mph (113 km/hr) toppled trees and caused tens of thousands of customers to lose power in the mid-Atlantic region, New York, Vermont, and Connecticut. At least three people were killed.

Unusually warm air fueled strong storms in the midwestern and southern U.S. on December 31st, producing high winds and a preliminary count of 53 tornadoes across five states. At least eight people were killed in Missouri and Arkansas and dozens of others were injured. In Mississippi, about 200 people were evacuated from the Jackson-Evers International Airport, where an EF-2 tornado crossed a runway. More detailed information is available in the NCDC December 2010 State of the Climate Tornadoes report.

Tropical Cyclone Tasha formed off the coast of northeastern Australia on December 24th. The storm made landfall early the next day between Cairns and Innisfail as a Category 1 cyclone with wind gusts of roughly 65 mph (105 km/hr) reported just offshore. Although the storm intensity quickly dissipated over land, it brought heavy rainfall to an already soaked region, resulting in more than an estimated $5 billion U.S. dollars in damages. The storm triggered flash floods, leading 41 local governments to declare disasters as mining and agricultural activities were disrupted. Some areas received about 20 inches (more than 500 mm) of rainfall from the 23rd–25th. Following its wettest spring (September–November) on record, the precipitation from Tropical Cyclone Tasha led to one of the most significant flooding events in Queensland's history as river catchments were overwhelmed in many areas, according to the Bureau of Meteorology. At least nine people were killed and up to 200,000 people were affected. The towns of Theodore and Condomine were completely evacuated. Residents of Rockhampton were also forced to leave as the town's river was expected to peak at 31 feet (9.4 meters) in early January, threatening 2,000–4,000 homes. Flooding closed more than 300 roads, including two major highways to the state capital of Brisbane. A vast area the size of France and Germany combined was inundated by the floodwaters. The rainfall from the storm, in combination with additional rainfall during the month led to Queensland's wettest December on record—an average of 8.25 inches (209.45 mm) across the state, well more than double the 1961–1990 December average of 3.25 inches (82.48 mm). The excessive rainfall was attributed to a strong La Niña.

Cold Arctic air gripped western Europe during most of the first three weeks of December. Two major snowstorms, icy conditions, and frigid temperatures wreaked havoc across much of the region. Over the course of the period, airports in the UK, Germany, France, the Netherlands, Belgium, and Switzerland were forced to cancel or delay thousands of flights, stranding tens of thousands of passengers. Further, railways and bus services were disrupted, stranding thousands more, and thousands of schools were closed. The first storm that occurred at the beginning of the month was reported to be Britain's heaviest and most widespread snow since 1993. Denmark mobilized its army to assist emergency vehicles in the southeastern portion of the country. On the 3rd, severe frost left 150,000 people without heat in the southern Polish city of Czestochowa. Paris, France—a city that typically sees rain—received 4 inches (10 cm) of snow on December 8th. Bus services were halted and the Eiffel Tower was closed for a day. That same day, Scotland saw its heaviest snowfall since 1963 and subsequently called on its army to help clear snow and ice. Thirty inches (75 cm) of snow fell in parts of the capital city of Edinburgh. Another round of heavy snow fell across Europe on the 17th–18th, forcing thousands more flight cancellations. According to its website, Heathrow Airport in London—the world's busiest international airport—was forced to close on the 18th as five inches of snow reportedly fell in one hour. Train and bus cancellations and delays in the UK, Germany, France, Belgium, and the Netherlands compounded woes for holiday travelers. Italy's island of Capri recorded its first snowfall in 25 years. Snow and icy conditions along with cold temperatures continued to wreak havoc across northern Europe on the 19th–20th as hundreds more flights were cancelled, rail services were disrupted, and schools were closed. Media reports said that Northern Ireland was experiencing its worst weather in 25 years. On the 18th, the temperature dropped to -0.4°F (-18°C) at Castlederg, County Tyrone, the lowest temperature ever recorded in Northern Ireland. The previous record low was 0.5°F (-17.5°C), set on January 1st, 1979 in Magherally. Within the past month, 114 people died in Poland due to the frigid temperatures and dozens of others were killed in weather-related accidents across Europe, according to multiple media reports. By the end of the month, the UK had experienced its coldest December in more than 100 years, with average temperatures about 9°F (5°C) below normal. The harsh winter weather was attributed to a negative Arctic Oscillation, which is a climate pattern that influences weather in the Northern Hemisphere. A very persistent, strong ridge of high pressure, or 'blocking system', near Greenland allowed cold Arctic air to slide south into Europe.

Europe was not the only region in the Northern Hemisphere affected by the Arctic Oscillation. A large snow storm and frigid temperatures affected much of the Midwest United States on December 10th–13th.
The storm brought 17.1 inches (43.1 cm) of snow to the Minneapolis/St. Paul region on the 10th–11th. According to the Minnesota State Climatology Office, this was the largest December snow storm for the area on record, the largest for any winter month since 1991, and the fifth largest since records began in 1891. The snow proved to be too much for the Minneapolis Metrodome's inflatable roof; it collapsed under the heavy weight of the frozen precipitation on the 12th. Eau Claire, Wisconsin received 22.0 inches (55.9 cm) of snow on the 11th, its highest single calendar day snowfall total in history. In the U.S., the storm also wreaked havoc across Indiana and Michigan. At least 16 people were killed in weather-related accidents. The storm moved east into southern Ontario, Canada, where two days of blizzard conditions stranded hundreds of vehicles on highways and secondary roads. One of the motorists reportedly died of hypothermia.

The same storm that wreaked havoc in the U.S. Southwest, Midwest, and South also brought up to 32 inches (81 cm) of snow and created blizzard conditions across parts of the eastern U.S. on December 25th–27th, a major national holiday weekend. A state of emergency was declared in North Carolina, Virginia, Maryland, New Jersey, Massachusetts, and Maine. In New York City, up to 24.5 inches (62 cm) of snow fell, effectively shutting down rail lines, major airports, and bus services. Thousands of flights were cancelled and stranded subway riders were forced to spend a night in unheated train cars. One person was reported killed in Maine due to the weather conditions.

In early December, NOAA proposed listing four subspecies of the ringed seal—Arctic, Okhostk, Baltic, and Lagoda—and two subspecies of bearded seals as threatened under the Endangered Species Act. These ringed seals are found in the Arctic Basin and North Atlantic, and bearded seals are in the Pacific Ocean. NOAA cited threats posed by declining sea ice and reduced snow cover. Ringed seal pups are typically born in snow caves during spring and are vulnerable to freezing and predators without them. These seals only produce a single offspring per year, which may limit their ability to respond to changing environmental conditions such as sea ice melt and snow cover. Bearded seals need sea ice, particularly during reproduction and molting stages. Models predict that the seasonal ice will be substantially reduced during this century, thus impacting the potential survival of the ringed seals.

National Snow & Ice

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

December brought near normal temperatures and precipitation when averaged over the entire U.S., but there was significant regional variability. The West and Southwest were warmer than average while the Northern Plains, Midwest, Mid-Atlantic, and Southeast were cooler than average. Precipitation amounts were also mixed across the country, with drier-than-average conditions for the South, Southeast, and Ohio River Valley, while it was a wet month for the West, Northern Plains, and parts of the Northeast. These conditions led to above average snow cover during December; the month ranked as the seventh largest December snow cover extent for bthe contigous U.S. on record (out of 45 years). According to the Rutgers Global Snow Lab, a NOAA supported facility, the monthly snow cover extent was 0.9 million square km (347,500 square miles) above the long term average of 2.9 million square km (1.1 million square miles). Above average snow extent occurred across the eastern and northern regions and intermountain west; below-average snow fell across the Southern and Central Plains. At the beginning of the month, 34.2 percent of the country was under snow cover — the high elevations of the West, the Northern Plains, and northern New England. Several winter storms impacted the U.S. during December increasing the amount of the country under snow to a monthly maximum of 55 percent on the 27th. On the last day of the month, 51 percent of the country was under snow — the higher elevations of the West, the Northern Plains, the Great Lakes, the central and southern Appalachians, the Mid-Atlantic Coast and most of the Northeast.

A strong blizzard hit Minnesota, Iowa, and Wisconsin on December 10th through 12th, bringing over a foot of snow to the region and sustained winds of 35 mph (56 km/hr). The 17 inches (43 cm) of snow that fell in Minneapolis was the 5th largest snowstorm ever for the city and the largest December snowfall on record. Minneapolis set a new December snowfall record with a monthly total of 33.6 inches (86 cm), the previous December record was set in 1969 when 33.2 inches (85 cm) of snow was reported. Data for the city goes back to 1884. The 22 inches (56 cm) which fell in Eau Claire, Wisconson on the 11th is the highest single calendar day snowfall total in history. An unusual aspect of the storm was the high snow-to-water equivalent of 9:1, which represents how heavy the snow was. The heavy nature of the snow, as well as the amount and strong winds, contributed to the collapse of the Metrodome roof, home to several professional sports teams. Fortunately the building was empty, and no one was injured.

During December a series of storms made landfall along the Pacific Coast, bringing with them a surge of moisture from the tropics often referred to as an atmospheric river or the 'Pineapple Express' since the deep moisture originates near Hawaii. The first storm impacted the Pacific Northwest on December 11th-12th, bringing heavy snowfall and rain. Daily rainfall records were broken in Seattle and flooding was widespread in Washington. The second system brought a significant influx of moisture to Southern California, Arizona, Colorado, Nevada, and Utah on December 19th through 22nd. Daily and monthly precipitation records were broken across the region. In California, snow accumulation up to 17 feet (5.2 meters) was reported in Sequoia National Park as well as 26 inches (660 mm) of rainfall in Crestline, California and a wind gust of 68 mph (110 km/hr). For the month, 10.23 inches (260 mm) of rain was reported in Downtown Los Angeles, marking the second wettest December on record behind December 1889 when 15.8 inches (401 mm) of rain fell in the city. Records in Los Angeles date back to 1877. Mammoth Mountain in California received 208 inches (528 cm) of snow for the month, breaking the previous December record of 139.8 inches (356 cm) which fell during December 1971. According to the resort website, the snow during the month caused Mammoth Ski Resort have more snow on the ground than any other ski resort in the world. The heavy rain and snow in the region caused Nevada and Utah to have their wettest December on record; while California and Oregon both had a top ten wet December. The same system moved into the Northern Plains of the U.S. causing blizzard conditions for the Dakotas and western Minnesota the last two days of the month. Wind gusts over 45 mph (72 km/hr) were reported and snowfall amounts over a foot (30 cm) were widespread over the Northern Plains. The same system was responsible for a significant tornado outbreak for central and southern parts of the country. See the December tornado report for more information.

24-28 December Snowfall

A low pressure system moved across the southern U.S. and interacted with another system moving from the Northern Plains the last week of December. The two systems brought widespread snowfall from Minnesota, southward to Alabama and Georgia and along the Eastern Seaboard to Maine on December 24th through 28th. Many locations in the Southeast experienced their first white Christmas on record, and many cities broke daily snowfall records because of the storm. As the system moved up the Atlantic Coast, it strengthened bringing heavy snowfall to the major cities in the Northeast. Central Park in New York City received 20 inches (51 cm) of snow, marking the sixth largest snowfall there, while Boston received 18.2 inches (46 cm), the city’s eight biggest snow storm on record. The 20.1 inches (52 cm) which fell at the Atlantic City International Airport was a single snowstorm record. In Philadelphia, the 12.4 inches (32 cm) gave the city 67.3 inches (171 cm) of snow for the 2010 calendar year, the largest January–December snowfall amount on record, ahead of the 57 inches (145 cm) which fell in 1978. The preliminary NESIS score, which measures the impact of snow on population centers, was a Category 3 (major).

Tornadoes

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

According to data from the Storm Prediction Center (SPC), December 2010 was an above-average tornado month, with 59 preliminary tornado reports across the United States. The pending tornado count currently ranks as the fourth busiest December for tornado activity since records began in 1950, behind December 2002, 1982, and 1967. Most of the tornado reports (53) were from December 31st as a strong storm system moved across the central part of the country. The northern edge of the storm brought heavy snowfall to the Northern Plains and severe weather was widespread over the Mississippi River Valley. A rare tornado also hit western Oregon on the 14th as a strong storm system made landfall from the Pacific Ocean.

On December 14th, an EF-2 tornado hit Aumsville, Oregon damaging 50 structures and injuring two people. Storm surveys estimate that winds were between 110–120 mph (177 km/hr–193 km/hr) in the tornado, and the storm had a path width of 150 yards (135 m) and a path length of 5 miles (8 km). According to the National Weather Service, this was the first tornado to touch down in the state since December 9th, 2009. On average, Oregon experiences two tornadoes annually, while only four tornadoes have impacted the state since 2000.

A storm system moving through the center of the country brought a severe weather outbreak to the middle and lower Mississippi River Valley on December 31st. Fifty-three tornadoes were preliminarily reported across Arkansas, Missouri, Illinois, Louisiana, and Mississippi, marking the 5th most active tornado day during 2010. Four fatalities were reported in Arkansas, and four were reported in Missouri. A tornado outbreak this large during the month of December is uncommon — the 1980-2009 December monthly average tornado count is 23. The current record for the number of confirmed tornadoes during a single day during December is 34, which occurred on December 18th, 2002. Once the tornado count is confirmed, it is likely that this outbreak will rank as the largest single-day December outbreak on record. There were three EF-3 tornadoes confirmed with the outbreak — one near Macon, Mississippi; one near Sunset Hills, Missouri; and one near Cincinnati, Arkansas. An EF-1 tornado hit near downtown St. Louis, but no significant injuries were reported there.

Hurricanes & Tropical Storms

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Note:This report catalogs recent tropical cyclones and places each basin's tropical cyclone activity in a climate-scale context. It is not updated in real time. Users seeking real time status and forecasts of tropical cyclones should visit The National Hurricane Center.

Drought

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page. These filenames begin with "drd964x" and end with "txt".

A strong west-to-east flow in the jet stream circulation characterized the weather pattern over the contiguous United States for December 2010. Deep low pressure systems developed in this flow, resulting in intense winter storms across the nation and outbreaks of cold Canadian air, especially east of the Rockies. About a third of the country was covered in snow at the beginning of the month. The snow cover expanded and contracted throughout the month with the passage of several winter storms, reaching 39 percent coverage by December 6th, about 53 percent by the 19th, and 55 percent by the 27th. By the end of the month, more than 8 feet of snow covered higher parts of the Sierra Nevada, with moisture content more than twice normal for this time of year. December 2010 was the 7th snowiest December for the contiguous U.S. and for the North American continent, based on satellite observations of area covered that go back to 1966. The storm systems triggered deadly tornado outbreaks at the end of the month in the Midwest to Lower Mississippi Valley.

Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Two such large-scale atmospheric circulation patterns, which were dominant during November, continued in December. The first was the La Niña, which is the phenomenon created by cooler-than-average sea surface temperatures in the eastern tropical Pacific Ocean. La Niña is typically associated with wet conditions in the northern tier states and Ohio Valley this time of year, and warm and dry conditions in the southern tier states. The second atmospheric circulation index was the Arctic Oscillation (AO), which was negative during most of December and strongly negative during the last half of the month. A negative AO is typically associated with dry conditions in the Southeast (especially the Southern Plains to Lower Mississippi Valley) and colder-than-normal temperatures east of the Rockies at this time of year (November-January).

The temperature and precipitation pattern for December 2010 matched what is expected from the negative Arctic Oscillation, especially east of the Rockies. Florida and Georgia had the coldest December in the 1895-2010 record and the Carolinas (N, S) ranked 3rd coldest. A total of 11 states from the Ohio Valley to the Gulf Coast had the tenth coldest, or colder, December in 2010. Precipitation was below normal from the Southern Plains and Southeast to the southern Great Lakes, with Louisiana and Mississippi having the 3rd driest December and 4 other states ranking in the top ten driest category. As a result, drought expanded in the southern tier states, especially the Southern Plains and Southeast. By the end of the month, 24 percent of the contiguous U.S. was classified in moderate to extreme drought, according to the USDM. The precipitation pattern over the West reflected a combination of La Niña and Arctic Oscillation influences.

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months. As seen on the Palmer Z Index map, low precipitation resulted in dry conditions for December 2010 much of the Southern Plains, Southeast, and Ohio Valley, and southern parts of the Great Lakes and Southwest. Wet conditions are evident on the Z Index map across the northern Plains and much of the West. These moisture anomalies persistently built up throughout the month (Palmer Z Index map for December 10, 15, 20, 25, 31). Compared with the November 2010 PHDI map, the December 2010 PHDI map indicates that drought conditions intensified in the Southeast, Lower Mississippi Valley, and Ohio Valley; drought conditions lingered in parts of the Mid-Atlantic region; and wet conditions intensified in the West and Northern Plains. The November 2010 PHDI map also reflects the long-term nature of the drought conditions. The Z Index and PHDI maps in combination show that the dryness in the Southeast, Lower Mississippi Valley, Ohio Valley, and around Delaware is both a short-term and long-term phenomenon, and that the dryness in the Southern and Central Plains is a short-term phenomenon.

Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months. Dryness is evident across the Central and Southern Plains at 1-, 2-, and 3-month time scales, and in southern portions of the Southwest for most time scales from 1 to 24 months. The Southeast to Lower Mississippi Valley are very dry from 1 to 12 months, with some evidence of dryness even at 24 months. Dryness in the Ohio Valley is evident at 1, 3, and 6 months, while the parts of the Great Lakes are dry at 1 to 3 months. Mid-Atlantic coast dryness shows up to some degree in the 1-month to 12-month maps. Wet conditions dominated the Northern Plains and parts of the Northeast at all time scales and much of the West for the last 1 to 12 months.

Agricultural Indices

December 2010 NLDAS ensemble-mean model soil moisture anomalies for the top 1 meter of soil

Vegetation Drought Response Index (VegDRI), December 26, 2010

Abnormal dryness and drought were evident in several indicators. There were hardly any days with rain from the Southern Rockies to the Southern and Central Plains, much of Florida, and parts of northern Minnesota and the Mid-Atlantic to southern New England states. This resulted in long runs of consecutive dry days in some of these areas. It is also reflected in low total precipitation amounts and below-normal precipitation. On the other hand, it rained or snowed most days of the month along northern parts of the Pacific coast. During the winter cold season, vegetation goes dormant across much of the country. But soil moisture, as monitored by several models (NOAA Climate Prediction Center [CPC] anomalies and percentiles, NLDAS [North American Land Data Assimilation System] top soil layer and total soil layer, VIC [University of Washington Variable Infiltration Capacity macroscale hydrologic model]), was still drier than average across much of the country from the southern Great Lakes to the Lower Mississippi Valley, across most of the Gulf Coast, and across parts of the central and southern Rockies and Plains. Satellite monitoring of vegetation health (Vegetation Drought Response Index [VegDRI] [December 26, January 2], Vegetation Health Index [VHI]) indicated stress on vegetation in parts of the Southwest, southern Plains, and Southeast.

On a statewide basis, December 2010 was drier than normal for many states in the Southern and Central Plains, Southeast, Mid-Atlantic, Ohio Valley, and southern Great Lakes. Five states had the tenth driest, or drier, December in the 1895-2010 record, including Louisiana and Mississippi which each ranked third driest. December was record dry for several climate divisions in the Lower Mississippi Valley (Louisiana climate divisions 1, 2, and 3, and Mississippi climate divisions 7, 8, and 10).

Dryness in the Southern Plains and Southeast to Ohio Valley has persisted for much of the last three months. Seven states had the tenth driest, or drier, October-December in 2010, with Florida ranking as the driest in the 1895-2010 record. October-December 2010 was record dry for several climate divisions in the southern regions (Texas climate divisions 5 and 10, and Florida climate divisions 2, 3, 4, and 5). Florida also had the driest July-December on record.

The Lower Mississippi Valley has suffered from deficient precipitation for most of the last 12 months. Statewide, Louisiana had the fifth driest year in the 1895-2010 record, Arkansas ranked ninth driest for 2010, and Mississippi eleventh driest. It was the driest year on record for several climate divisions (Louisiana climate divisions2, 3, and 4, Mississippi climate division 4, and Arkansas climate division 8).

Percent area of the Western U.S. in moderate to extreme drought, January 1900-December 2010, based on the Palmer Drought Index.

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.

As noted by the Southeast Regional Climate Center, monthly precipitation was below normal (generally less than 50 percent) across nearly the entire region in December. A large portion of the monthly rainfall came on the 1st of the month as a line of strong storms moved through the Southeast and mid-Atlantic regions. The driest locations across the Southeast (less than 25 percent of normal) were found in central and eastern Florida, southern Alabama, central portions of Georgia and the Carolinas, much of the southern Appalachian Mountains, and the Shenandoah Valley of Virginia. Sanford, Florida, located northeast of Orlando, recorded 0.15 inch (3.8 mm) of precipitation for the month, which was only six percent of normal. Montgomery, Alabama [1.03 inches (26.2 mm)] and Columbus, Georgia [1.56 inches (39.6 mm)] experienced their 2nd driest December in records extending back to 1871 and 1947, respectively. In contrast, monthly precipitation totals were between 150 and 300 percent of normal across the northern coast of Puerto Rico. San Juan recorded 7.47 inches (189.7 mm) of precipitation for the month, which was 2.9 inches (73.7 mm) above normal. It was the driest year on record in the Jacksonville Beach, Florida area with a preliminary annual total of 28.44 inches (722.4 mm). Conversely, San Juan, Puerto Rico recorded its wettest year on record with 89.51 inches (2274 mm), eclipsing the previous record of 87.55 inches (2224 mm) set in 1931.

Monthly average temperatures for December 2010 were well below normal across the Southeast region. The greatest departures occurred throughout Florida and eastern sections of Georgia, the Carolinas, and Virginia, where monthly average temperatures were 9 to 11 degrees F (5.0 to 6.1 degrees C) below normal. Interior portions of the Southeast were generally 6 to 9 degrees F (3.3 to 5.0 degrees C) below normal, while much of Alabama and northern Virginia were 5 to 6 degrees F (2.8 to 3.3 degrees C) below normal. Over 70 locations in the Southeast experienced their coldest December on record. Across the Southeast, over 1,100 daily low maximum temperature records and over 800 daily minimum temperature records were tied or broken during the month. Jacksonville, Florida recorded 19 days of subfreezing minimum temperatures during the month, which shattered the old record of 12 set back in 2000. The frigid air masses that predominated across the Southeast also influenced parts of the Caribbean; monthly average temperatures were below normal across Puerto Rico and as much as 4 degrees F (2.2 degrees C) below normal on the U.S. Virgin Islands.

Despite the overall lack of precipitation during the month, the coverage of abnormally dry (D0) and drought conditions (D1 or greater according to the U.S. Drought Monitor) across the Southeast decreased from 87 percent at the end of November to 77 percent at the end of December. Areas of abnormal dryness (D0) were eliminated across parts of Virginia, western and eastern North Carolina, western Alabama, and northeast Georgia. In addition, moderate drought (D1) conditions expanded slightly into parts of central North Carolina and south Florida, while extreme drought (D3) conditions expanded across northeast Florida and southeast Georgia. The cold temperatures severely disrupted the planting of winter vegetables (e.g. peppers and onions) in parts of Florida and Georgia and resulted in a state of emergency declaration in Florida to ensure that the harvesting and transport of fall crops were not delayed on account of the cold weather.

As explained by the Southern Regional Climate Center, December precipitation totals were quite low over most the Southern region. For the majority of the region, this was the third consecutive dry month. In December, the majority of the region received less than half of the monthly normal precipitation. Louisiana reported a state average monthly total of only 1.85 inches (46.99 mm), which is the third driest December on record (1895-2010). Likewise, Mississippi experienced its third driest December on record with a monthly precipitation total of only 1.45 inches (36.83 mm). Arkansas also reported a monthly precipitation total of 1.45 inches (36.83 mm), which makes it their eighth driest December on record. Texas recorded its eleventh driest December, with a monthly precipitation total of 0.67 inches (17.01 mm). Tennessee reported its eighteenth driest December, while Oklahoma reported its thirty-first driest December. The state average precipitation total in Tennessee was 2.76 inches (70.10 mm), while Oklahoma reported a value of 0.93 inches (23.62 mm). The driest areas of the Southern region included much of western Texas, southern Texas, northern Louisiana, and southern Arkansas. In these areas, most stations reported less than a quarter of the monthly normal precipitation totals. In the case of west and southern Texas, many stations recorded less than one tenth of an inch (2.54 mm) for the month. December average daily temperatures varied spatially throughout the Southern region, with a strong gradient from west to east. The western states experienced a slightly warmer than normal month, while eastern and central states experienced a much cooler than normal month.

A third consecutive month of dry conditions in the Southern region has resulted in a wide expansion of drought conditions. As of December 28, 2010, 67.65 percent of the Southern region was experiencing moderate drought or worse; 35.21 percent was in severe drought or worse, and 10.17 percent was classified as extreme drought conditions. This is a dramatic change from November. For instance, on November 30, 2010, the aforementioned values were 41.2 percent, 19.3 percent, and 2.7 percent, respectively. The most significant changes are seen in the central counties of eastern Texas where extreme drought was introduced. There was also a westward expansion of severe drought into the western parishes of Louisiana.

As summarized by the Midwest Regional Climate Center, Midwest precipitation totals varied widely in December. Above-normal precipitation fell in the northwest quarter of the region with west-central Minnesota receiving nearly five times their normal precipitation. Eastern Kentucky was also slightly above normal. The areas in between received less than normal precipitation with a swath from Missouri to Lake Huron at less than half of their normal. Snowfall was especially heavy in Minnesota, western Wisconsin, and northeast Iowa. Above-normal snowfall also fell along a narrow swath extending from southern Minnesota to eastern Kentucky. Three different storms tracked along this path during the month. 2010 annual precipitation was above normal for most of the western half of the Midwest with south-central Iowa more than 20 inches (508 mm) above their normal for the calendar year. Southeast Missouri and along the Ohio River to Cincinnati were 6 inches (152 mm) to 10 inches (254 mm) below normal for their 2010 annual precipitation.

December temperatures were colder than normal across the Midwest. Departures from normal ranged from 0 °F (0 °C) in the upper Midwest to as much as 10 °F (6 °C) below normal in eastern Kentucky. Maximum temperatures were even colder ranging from 1 °F (1 °C) to 14 °F (8 °C) below normal. Kentucky recorded its first colder-than-normal month since February 2010. The year was near normal for most of the Midwest with only the northern parts of Minnesota, Wisconsin, and Michigan averaging 2 °F (1 °C) to 4 °F (2 °C) above normal.

As noted by the Northeast Regional Climate Center, December's precipitation totals varied throughout the region, with 5 states averaging drier than normal and 7 states on the plus side. The regional average was 3.82 inches (97 mm), which was 113 percent of normal. Once again, Maine was the wettest state in the region, with 175 percent of the normal amount of precipitation. Delaware, with only 42 percent, had its 10th driest December since 1895. Annually, precipitation totals evened out, leaving the region at exactly 100 percent of normal. Yearly departures among the states ranged from 87 percent of normal in Delaware to 115 percent in Maine.

Temperatures during December 2010 averaged below normal for the first time since December 2009. The Northeast's monthly average of 25.4 degrees F (-3.7 degrees C) was 3.0 degrees F (1.7 degrees C) below normal and 2.4 degrees F (1.3 degrees C) cooler than December 2009. It was the coldest December in the region since 2000. A cool December could not offset the previous eleven months of above normal temperatures. With an annual average of 49.2 degrees F (9.6 degrees C), 2010 became the 5th warmest year in the Northeast since recordkeeping began in 1895. Two states, New Hampshire and Rhode Island, had their warmest year on record. Of the remaining states, all but West Virginia had annual temperature averages that placed them in the top 20 warmest since 1895.

As explained by the High Plains Regional Climate Center, southern portions of the region, including Kansas, Nebraska, and eastern Colorado, received little to no precipitation in December. This caused existing drought conditions to persist and led to the development of drought in eastern Kansas as well. While the southern portion of the region remained dry, several storm systems impacted the northern portions this month. The Dakotas were hit particularly hard by heavy snowfall which set new records and impacted travel. Several areas of both North Dakota and South Dakota had liquid equivalent precipitation totals which were over 400 percent of normal. Temperatures across the High Plains region this month were below normal in the eastern half and above normal in the western half. The dividing line between the above and below normal temperatures ran from southwestern South Dakota into central Nebraska, and then into west-central Kansas.

According to the USDM, drought conditions deteriorated across the southern portions of the region this month. By the second week of December, abnormally dry conditions (D0) had expanded north from Oklahoma into eastern Kansas and severe drought conditions (D2) had expanded from eastern Colorado into western Kansas. In addition, D0 had spread further east in Nebraska. By the end of the month, moderate drought conditions (D1) had developed in eastern Kansas as well. Only slight improvements were seen in extreme northwestern Colorado where the D0 area was eliminated and in western Wyoming where the D1 and D0 areas were trimmed due to heavy snowfall.

As summarized by the Western Regional Climate Center, precipitation was well above normal throughout the region except for Southern Arizona and New Mexico and Eastern Colorado. Many parts of southern and central California received their wettest December ever. It was the second wettest December on record in downtown Los Angeles dating back to 1889. Bishop, California, received 105 percent of their annual average in 3 days (18-20th). Up to 29 inches of rain in the San Gabriel and San Bernardino Mountains of Southern California for the month, most of it within a 6-day period from the 17th-22nd. Bakersfield's (California) total of 5.82 inches (148 mm) not only broke a December record but an all-time monthly record going back to 1893. New December records were also set in portions of Southern Nevada and Utah. St. George Utah had their wettest December on record dating back 117 years. Over 15 inches (381 mm) of precipitation fell at Mt. Charleston, Nevada, while Ely, Nevada recorded their wettest and snowiest December in 85 years of data. Snowpack in the Sierra Nevada of California and a broad swath northeast to the upper Colorado River Basin was over 200 percent of normal by the end of the month, and the rest of the West except Washington was reporting a snowpack of well over 100 percent. Meanwhile, in Honolulu, rainfall for December was the greatest since 1987 (11.73 inches, 298 mm) and provided 67 percent of their 2010 annual total. Much of that (5.41 inches, 137 mm) fell in one day (on the 19th). Except for Montana, nearly the entire West observed above normal temperatures, especially southeast New Mexico and the Front Range of Colorado. Fairbanks, Alaska, on the other hand, had its coldest December since 1980. Had it not been for extremely cold temperatures the final two days of the month, many locations would probably have broken records for December warmth.

Upper Colorado River Basin: As reported by the Colorado Climate Center, the late December-early January NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that most of the Upper Colorado River Basin (UCRB) received near or above average precipitation for November, while areas east of the UCRB remained dry -- a pattern that continued through December. As of December 28th, all of the sub-basins of the UCRB had above average snowpack and precipitation for the current water year (October 1-December 28), with only a few individual sites slightly below average. Most of the western portions of the UCRB had snow water content near the 100th percentile, meaning that very few to no years have been as wet by this time as the current water year. Averaged across the UCRB, water-year-to-date (WYTD) precipitation was at 147 percent of average and snowpack was at 142 percent of average. As of December 26th, about 92 percent of the USGS streamgages in the UCRB recorded normal (25th to 75th percentile) or above normal 7-day average streamflows. While recent flow conditions have been good, total cumulative runoff from the upper basin to the lower basin for the 2010 calendar year will be substantially less than the historical average. For the month of December, temperatures were around 6 degrees F warmer than average through much of the UCRB. While temperatures have been warm, the air has been moist with a persistent flow of moist Pacific air for most of the month. Soil conditions improved in northeastern Utah, the Four Corners region and western Wyoming, but soils dried east of the UCRB throughout eastern Colorado. Reservoir levels were above average for this time of year at Blue Mesa, Flaming Gorge, Navajo Lake, and Lake Granby. Lake Powell's storage decreased in December, with its lake level at 77 percent of average for this time of year and around 60 percent of capacity.

Pacific Islands: According to reports from National Weather Service offices, the Pacific ENSO Applications Climate Center (PEAC), and partners, conditions varied across the Pacific Islands.

Drought conditions eased significantly across most of Hawaii during December. Kauai County and Oahu received the highest rainfall totals, eliminating drought in both areas. While the Big Island received lower amounts of rainfall, improvements were most significant here and included the elimination of exceptional drought (D4). Exceptional drought conditions were in place since March 2, 2010. The area of extreme drought (D3) was also reduced significantly and covered just the upper leeward slopes from Ahumoa to Pohakuloa. Severe drought (D2) surrounded the D3 area and extended northwestward to Kawaihae and southwestward into the central Humuula Saddle. A separate area of severe drought covered the southern portion of the Kau District from Manuka to Naalehu. For Maui County, areas of D3 conditions in Lanai, western Molokai, and leeward Maui have all been changed to D2 conditions. East Molokai and the windward portions of Maui were free of drought.

Some drought impacts in Hawaii include the following:

Water levels in the Waimanalo Reservoir on Oahu increased considerably over the past month. The State of Hawaii Department of Agriculture eased water use restrictions, going from a mandatory 30 percent cutback to a 20 percent cutback on December 21.

Pastures and general vegetation conditions on Molokai have improved due to recent rainfall. Water levels in the Kualapuu Reservoir increased modestly but not enough to warrant any easing of the 30 percent cutback in irrigation water consumption.

Above-normal rainfall produced an improvement in conditions on Lanai. Previously, drought conditions forced cattle ranchers to ship feed from off-island which resulted in financial impacts.

Pastures in leeward Maui improved over the past month but more rainfall is needed for a full recovery. Water supply levels remained sufficient for upcountry Maui. However, as a precaution, the Maui County Department of Water Supply continued to request a 5 percent reduction in water use by upcountry residents. A 10 percent reduction in water use by Central and South Maui residents also remained in effect.

On the Big Island, pastures in the lower slopes of the South Kohala District and the southern portion of the Kau District improved during December. However, some ranchers were still hauling water to support livestock. Additional rainfall is needed in the coming months to produce a full drought recovery.

On other Pacific Islands, drought conditions continued near the equator. Although adequate rain from showers and occasional thunderstorms have occurred north of 3 degrees North latitude, strong subsidence associated with the moderate to strong La Niña has suppressed rainfall in areas closer to the equator. Drought conditions extended from about 150 degrees East longitude to at least the International Date Line. This area includes Kapingamarangi Atoll, Nauru, and the atolls of western Kiribati.

In the Federated States of Micronesia, adequate rainfall has occurred for most of Pohnpei state, but weather has remained very dry at Kapingamarangi over the last 5 to 6 months (Kapingamarangi is a southern island in Pohnpei state, near the equator). Kapingamarangi received only 0.76 inch of rain in December, which is 9 percent of average. The total rainfall for August-December 2010 was 7.81 inches, or 24% of average. Some damage to food crops may have occurred on Kapingamarangi Atoll as a result of the drought, so close monitoring of the health of food crops was recommended. Continued implementation of stringent water conservation measures on the island was also encouraged. Rainfall at Nukuoro was barely sufficient in December with only 3.85 inches, or 35 percent of average. For August-December, Nukuoro has received 40.13 inches of rain (73 percent of average). At Kosrae, December rainfall was 10.99 inches (72 percent) and August-December rainfall totaled 53.98 inches (79 percent). The statewide average for Pohnpei was 80 percent of normal for December and 87 percent of normal for August-December.

Global Snow & Ice

NH Snow Cover Extent

The Northern Hemisphere snow cover extent during December 2010 was much above-average, marking the fourth largest December snow cover extent on record — behind December 2009, 1985, and 1970. The December 2010 snow extent for the Northern Hemisphere was 2.4 million square km (0.9 million square miles) above the long-term average of 43.3 million square km (16.7 million square miles). Eurasia and North America both had above-average snow cover during the month. Numerous large winter storms occurred across the western and eastern United States and Western Europe. Please see the December 2010 Global Hazards report for additional information on these individual storms. According to a satellite analysis by the Rutgers Global Snow Lab, above-average snow cover was reported across eastern and western North America, most of Europe, and western Asia during December. Below average snow cover was reported for the central U.S. and across eastern and central Asia.

During December 2010, the North American snow cover extent was above average, ranking as the seventh largest on record. This marks the fourth consecutive December with above-average snow cover extent for the continent. The monthly average extent was 1.0 million square km (0.4 million square miles) above the long term average of 16.6 million square km (6.4 million square miles). According to data from the Rutgers Global Snow Lab, Canada, the contiguous U.S., and Alaska all had above-average snow coverage for the month. Cool conditions dominated the eastern U.S. and numerous storms affected the West coast contributing to the U.S. having much-above-average snow cover for the month. Several U.S. cities broke December monthly snowfall records — please see the December 2010 U.S. snow report for additional information.

Eurasian snow cover extent during December 2010 was also above average, ranking as the sixth largest on record. This is the second consecutive December with above-average snow cover extent for Eurasia, with snow and cold dominating the weather pattern across Western Europe during the month. The December 2010 Eurasian snow cover extent was 1.4 million square km (0.5 million square miles) above the long term average of 26.6 million square km (10.3 million square miles).

Sea Ice Extent

According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent — which is measured from passive microwave instruments onboard NOAA satellites — averaged for December 2010, was 12.0 million square km (4.63 million square miles), 10.2 percent below the 1979-2000 average. This is the smallest December Arctic sea ice extent since records began in 1979. The December 2010 ice extent was 270,000 square km (104,000 square miles) smaller than the previous record low December extent in 2006. Arctic sea ice during December was below average on both the Atlantic and Pacific sides of the Arctic. Hudson Bay was particularly noteworthy because it was still not completely ice covered by the end of December, with the ice coverage roughly 50 percent of normal for the month. The bay is typically completely ice covered by the end of November. Northern Hemisphere ice extent for December has decreased at a rate of 3.4 percent per decade.

The below average Arctic sea ice was at least partially attributable to above-average air temperatures over Eastern Canada, Greenland, and eastern Siberia. Temperatures in these regions ranged from 6 to 10 degrees C (11 to 18 degrees F) above normal during December and sea ice coverage in these regions was below average. Meanwhile, temperatures were below-average for parts of Alaska and Scandinavia during December, and ice extent in these regions was near-to-above normal. These temperature patterns are associated with the strongly negative phase of the Arctic Oscillation, which dominated the weather pattern for the Northern Hemisphere high and middle latitudes during December. Abnormally high pressure was anchored over Eastern Canada and Greenland as well as the far northern Pacific Ocean. This pressure pattern contributed to the warmer-than-average temperatures across regions of the Arctic.

Conversely, during December 2010, the Southern Hemisphere sea ice extent was 8.87 percent above the 1979-2000 average. This was the sixth largest December Southern Hemisphere sea ice extent on record, and the fourth consecutive December with above-average ice extent. December Antarctic sea ice has increased at an average rate of 1.6 percent perdecade. Antarctic sea ice usually expands during the cold season to a September maximum, then contracts during the warm season to a March minimum.

Upper Air

Contents of this Section:

Note: Beginning in December 2010, all lower troposphere, middle troposphere, and lower stratosphere satellite data are reported here with respect to the 1981–2010 base period. Prior to December 2010, data were reported with respect to the 1979–1998 base period. Remote Sensing Systems continues to provide data to NCDC with respect to the 1979–1998 base period; however, NCDC readjusts the data to the 1981–2010 base period so that the satellite measurements are comparable.

Upper Air Highlights

University of Alabama Huntsville satellite analyses report a lower-troposphere December temperature anomaly of 0.18°C (0.32°F) above normal, the seventh warmest since satellite records began in 1979. For the period January–December 2010, the anomaly was 0.41°C (0.74°F) above normal and ranked as second warmest.

Remote Sensing Systems satellite analyses report a lower-troposphere November temperature anomaly of 0.14°C (0.26°F) above average, also the seventh warmest on record. For the period January–December 2010, the anomaly was 0.38°C (0.68°F) above average and ranked as second warmest.

For the year 2010 (January–December), radiosonde measurements indicate that global mid-troposphere temperatures were 0.78°C (1.40°F) above the 1971–2000 mean, the warmest on record.

University of Alabama Huntsville satellite analyses report a 2010 (January–December) mid-troposphere temperature anomaly of 0.32°C (0.58°F) above average, the second warmest such period on record. When these analyses are adjusted to remove stratospheric influence, the anomaly increases to 0.40°C (0.72°F), also the second warmest on record.

Remote Sensing Systems satellite analyses report a 2010 (January–December) mid-troposphere temperature anomaly of 0.33°C (0.59°F) above average, the second warmest such period on record. When these analyses are adjusted to remove stratospheric influence, the anomaly increases to 0.40°C (0.72°F), also the second warmest on record.

For the lower stratosphere, University of Alabama Huntsville report that December 2010 was the 17th coolest December since satellite records began in 1979. Remote Sensing Systems satellite analyses report that December 2010 was the 18th coolest such period.

Troposphere

Temperatures above the Earth's surface are measured within the lower troposphere, middle troposphere, and stratosphere using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and satellite records have been adjusted to remove time-dependent biases (artificialities caused by changes in radiosonde instruments and measurement practices as well as changes in satellite instruments and orbital features through time). Global averages from radiosonde data are available from 1958 to present, while satellite measurements date back to 1979.

Lower Troposphere

These temperatures are for the lowest 8 km (5 miles) of the atmosphere. Information on the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS) sources of troposphere data is available.

Mid-troposphere

These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 3–10 km [2–6 miles] above the Earth's surface), which also includes a portion of the lower stratosphere. (The Microwave Sounding Unit [MSU] channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 10 km [6 miles].) Because the stratosphere has cooled due to increasing greenhouse gases in the troposphere and losses of ozone in the stratosphere, the stratospheric contribution to the tropospheric average, as measured from satellites, may create an artificial component of cooling to the mid-troposphere temperatures. The University of Washington (UW) versions of the UAH and RSS analyses attempt to remove the stratospheric influence from the mid-troposphere measurements, and as a result the UW versions tend to have a larger warming trend than either the UAH or RSS versions. For additional information, please see NCDC's Microwave Sounding Unit page.

The radiosonde data used in this global analysis were developed using the Lanzante, Klein, Seidel (2003) ("LKS") bias-adjusted dataset and the First Difference Method (Free et al. 2004) (RATPAC). Additional details are available. Satellite data have been adjusted by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004)** to remove the influence of the stratosphere on the mid-troposphere value. Global averages from radiosonde data are available from 1958 to present, while satellite measurements began in 1979.

Radiosonde measurements indicate that, for 2010 temperatures in the mid-troposphere were 0.78°C (1.40°F) above average, resulting in the warmest calendar year (out of 53 years) since global radiosonde measurements began in 1958. This was the 25th consecutive calendar year with temperatures warmer than average. Meanwhile, satellite analyses of the January–December year-to-date period for the middle troposphere was second warmest in the 32-year satellite record.

As shown in the table below, global mid-troposphere temperature satellite measurements for December 2010 ranked 11th warmest to 17th warmest on record.

Stratosphere

The table below summarizes stratospheric conditions for December 2009. On average, the stratosphere is located approximately 16–23 km (10–14 miles) above the Earth's surface. Over the last decade, stratospheric temperatures have been below average in part due to the depletion of ozone. The large positive anomaly in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the sharp jump in temperature in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines. In both cases the temperatures returned to pre-eruption levels within two years.

December is not part of the active wildfire season across the western U.S., and little fire activity is expected during the month. December 2010 was not an exception. Between November 26th and December 30th, 5,826 fires burned 117,596 acres (28,219 hectares) across the United States. Weather conditions averaged for December indicated that the western and northern states were wetter than average, while the states across the South, Southeast, and Midwest were drier than average. Temperatures followed a similar spatial pattern — the West tended to be warmer than average while most of the central and eastern regions were cooler than average. See the national temperature and precipitation State of the Climate report for additional information on temperatures and precipitation. Wildfire activity during December was confined to the regions with the driest conditions. On December 10th, there were five large fires active in the U.S., three in Texas and one each in Oklahoma, and Florida. Fire activity picked up by the 23rd when ten large fires were active — three in Oklahoma and Florida, two in Texas, and one each in Arkansas and New Mexico. By the end of the month, fire activity continued to be confined to the driest regions of the country. Seven fires were burning on the 30th, three in Florida and two each in Oklahoma and Texas.

According to statistics from the National Interagency Fire Center (NIFC), at the end of December, 5,826 fires burned 117,596 acres (28,219 hectares), with an average of 20.2 acres (8.2 hectares) per fire. Fire activity was mostly confined to the South and Southeast regions of the country. The number of new wildfires was 45 percent above average while the number of acreage burned was 47 percent below average, continuing the 2010 annual trend of below-average acreage burned. Please visit the 2010 annual wildfire report on the overall fire conditions during 2010.

According to the U.S. Drought Monitor, the overall drought foot print increased during December from covering 14 percent of the country to covering 19.9 percent. The wet conditions improved the drought conditions across Utah, Nevada, and California, while conditions worsened across southern Arizona and New Mexico. The drier than average weather across the Southern Plains worsened the drought in most of Texas and Oklahoma by
one to three categories. Drought conditions also worsened for the Lower Mississippi River Valley, the Gulf Coast, and most of the Florida peninsula. Several weather systems moving through the Ohio River Valley improved drought conditions there one to two categories and ended drought in the central Appalachians. Conditions in the rest of the Southeast remained generally unchanged. The state of Hawaii saw a vast improvement in drought conditions where two frontal systems dropped several inches of rain on the parched archipelago. The abnormally dry regions in central Alaska also experienced improvement.

According to the U.S. Forest Service (USFS) Wildland Fire Assessment System, at the beginning of December regions experiencing high fire danger was consistent with the location of drier-than-average weather conditions. The highest fire danger was occurring across southern California and Arizona, stretching into central Texas. By the 15th, wet weather lowered the fire danger across the Southwest, while dry conditions intensified the fire danger across central and northern Texas. High fire danger was also reported across the piedmont of the Southeast. Precipitation during the last half of December limited the occurrence of high fire danger on the 30th to northern Texas.

According to the USFS Wildland Fire Assessment System, at the beginning of the month, low 10-hour fuel moistures were present across the Southwest, Southern Rockies, and the Southern Plains as well as the Florida and the Carolina Coast. Low 100-hour fuel moistures were widespread across the Southwest, Great Basin, and Southern Plains. Persistent wetness limited low 1,000-hour fuel moistures to the Southern Plains. On the 15th, precipitation across the West had moistened fuels there, with low 10-hour, 100-hour, and 1,000-hour fuel moistures were reported across southern Arizona, the Southern Rockies, and Southern Plains. Low 10-hour and 100-hour fuel moistures were widespread across Florida and the Mid-Atlantic. By the end of December, the low 10-hour fuel moistures increased across the West and Southeast with the only low 10-hour fuel moistures reported across the Southern Plains. Precipitation also limited low 100-hour and 1,000-hour fuel moistures across most of the country except for western Texas.

According to the USFS Wildland Fire Assessment System, at the beginning of the month, regions with high Keetch–Byram Drought Index (KBDI) values were consistent with regions experiencing drought. At the beginning of December, high KBDI values were reported across the Southwest, the Great Basin, most of Texas, the Lower Mississippi River Valley, the Southeast Coast, and the Florida Peninsula. By the 15th, conditions across the West remained generally unchanged, while high KBDI values increased in spatial extent across Texas and the Southeast. The widespread precipitation across the West during the last half of the month lowered the high KBDI values there. Only Texas and Florida reported high KBDI values by the 31st.